In the partial combustion of solid fuel a hot product gas is discharged from the reactor which contains considerable percentages of hydrogen and carbon monoxide and which contains ash and char particles. Considerable amounts of water, carbon dioxide and/or nitrogen (the latter if air is used as gasifying agent) may be present in the product gas as well.
Partial combustion is the reaction of all of the fuel particles with a substoichiometrical amount of oxygen, either introduced in pure form or admixed with other gases, such as nitrogen or steam, whereby the fuel is partially oxidized to hydrogen and carbon monoxide. This partial combustion thus differs from complete combustion wherein the fuel is completely oxidized to carbon dioxide and water.
During discharge of the product gas, the problem arises that the sticky ash particles are deposited on the walls of the outlet duct, where they will solidify. The outlet duct may thus clog up, in which case the process must be interrupted--which is unacceptable.
Examples of fuels that raise specific problems solved by the present invention are coal, brown coal or lignite, heavy hydrocarbon residues, tar sands, shale oils and petroleum coke.
In an attempt to solve the foregoing problem, applicant previously proposed forming a gas shield to protect the wall of the outlet duct. The product gas could then be cooled in the outlet duct to such an extent as to cause the ash particles to solidify and lose their stickiness before they hit a wall. According to that proposal, the protective gas shield was introduced via an annular slit at the upstream end of the outlet duct.
In certain cases, however, a gas shield so formed may be disturbed prematurely. For instance, when a flexible coupling has been installed between the reactor and the outlet duct, a lateral displacement may occur between the nozzle with which the reactor opens into the outlet duct and the duct itself, which displacement would give rise to disrupture of the gas shield further upstream in the outlet duct. Again, when several burners are placed in the reactor opposite each other and when a minor change in the position of one or more burners occurs there is also a chance of "oblique" loading of the product gas outlet duct and local disturbance of the gas shield formed in the manner according to the earlier proposal. Besides, in low-capacity reactors, for instance, the degree of out-of-roundness and the surface roughness of the gas outlet duct are found to be critical factors, as well as growth of deposits on the wall and mutilation of the surface by the breaking out of chips during use (e.g., by damage due to thermal degradation of the wall material).